Laser employing selected cyanogen halides as lasing gases

ABSTRACT

A gas laser utilizes essentially vibrationally excited nitrogen or carbon monoxide as an energizing gas and, through resonant collisions with a lasing gas, transfers the energy to the lasing gas, preferentially to an upper laser energy level. The lasing gas is a cyanogen halide including BrCN, C1CN or FCN, which is preferably introduced directly into the laser cavity free of prior excitation so as to avoid molecular decomposition. Laser energy at wavelengths between 5 and 10 microns is produced.

United States Patent Inventor Casper J. Ultee Glastonbury, Conn.

App]. No 811,700

Filed Mar. 27,1969

Patented Nov. 2, 1971 Assignee United Aircraft Corporation East Hartford, Conn.

LASER EMPLOYING SELECTED CYANOGEN Assistant Examiner-Joseph G. Baxter Attorney-Melvin Pearson Williams l-lAlLlllDES AS LASING GASES 1 cflaimzDrawing Figs. ABETRAIT: A gas laser utilizes essentially vibrationally excited nitrogen or carbon monoxide as an energizing gas and, U.S.Cl 331/94.5 through resonant collisions with a lasing gas, transfers the f H015 3/00 energy to the lasing gas, preferentially to an upper laser energy Field oil Search 331/945 leveL h l i gas i a o en halide including BrCN, R f d ClCN or FCN, which is preferably introduced directly into B enmes I e the laser cavity free of prior excitation so as to avoid molecu- UNITED STATES PATENTS lar decomposition. Laser energy at wavelengths between 5 3,435,363 3/1969 Patel 331/945 and 10 microns is produced.

JOMC 45 6 [fidffi 0/ f 7 7 a /qaewr {X67 /fl/l/ [flV/ l (WA/776 04 Jdueai/ BACKGROUND OF THE INVENTION Field of Invention This invention relates to gas lasers, and more particularly to a gas laser for producing radiation in the infrared.

Description of the Prior Art The mechanics of gas lasers are currently well known. A great deal of attention has been paid recently to the excitation of a lasing gas to an energy level capable of emitting photons and thereby participating in stimulated emission of coherent light within a laser cavity as a result of energy preferentially transferred to the lasing gas through near-resonant collision with a vibrationally excited energizing gas. One type of gas laser which has receiver a great deal of attention is the nitrogen-carbon dioxide laser. In this type of gas laser, the nitrogen is excited to the first vibrational level, and it transfers energy into the upper laser lever (001) of carbon dioxide preferentially, so as to provide a population inversion which supports laser emission. The emission of photons by the carbon dioxide causes the molecules thereof to assume the energy of the lower laser level (100) and molecules in this energy level rapidly decay via gas collisions to the ground state.

The method of exciting the energizing gas may vary in accordance with the particular design parameters of a given laser, as is known in the art. For instance, electric excitation may be utilized in any of several forms. One well-known form is radiofrequency excitation; another form is direct current plasma excitation; and a third known form is microwave excitation. Additionally, it is possible to excite the energizing gas by causing it to absorb intense light of a frequency matched to the spacing of the low-lying vibrational energy levels of the energizing gas. For instance, carbon monoxide may be raised to its first vibrational energy level by absorption of light with a wavelength of about 4.7 microns. Another known method of obtaining energizing gas in an excited state comprises the sudden cooling of a heated energizing gas. Thus, the energizing gas may be heated as a result of the utilization of any thermal source (such as the simple burning of fuel) or by a heating are, and it may thereafter be caused to flow through an expansion nozzle at supersonic speeds so as to freeze the energy in the lower vibrational levels of the energizing gas while translational cooling takes place, thus providing a highly nonequilibrium energy distribution with preferential excitation in the vibrational levels. In the preferred embodiment of the invention, gas temperatures equal to 1,000 deg. K or greater will be achieved in the energizing gas before expansron.

A recent advancement in the art comprises the technique of mixing, wherein the lasing gas is caused to mix intimately with the vibrationally excited energizing gas directly within the laser cavity to accomplish population inversion in the lasing gas so that the energizing of the lasing gas to its upper laser level or levels does not cause prelasing, and is not depleted by collisional energy transfers or other adiabatic phenomena prior to entrance into the laser cavity where the energy may participate in the generation of laser light.

In the aforementioned gas lasers, the wavelength of the laser radiation obtained depends upon the laser transitions between various energy levels. A great deal of work has been done with the carbon dioxide laser which produces laser light at 10.6 microns, and with other laser systems which produce light at various other wavelengths. These are well suited to some uses, but atmospheric absorption of light at certain frequencies limits their usefulness. Additionally, laser energy may be utilized for various useful processes, provided that light of a proper wavelength can be obtained.

It should be understood that the laser emission occurs over a band of wavelengths approximately centered on the wavelengths listed. Furthermore, due to uncertainties existing in the present art, only approximate assignments of these laser wavelengths can be made.

SUMMARY OF INVENTION The object of the present invention is to provide a laser capable of radiation at infrared wavelengths.

According to the present invention, a lasing gas comprising any of three Cyanogen Halides, BrCN, ClCN or FCN is energized to an upper laser energy level, whereby stimulated coherent emission of electromagnetic radiation or laser energy will result at infrared wavelengths. According further to the present invention, the lasing gas may be excited through nearresonant collisions with a vibrationally excited energizing gas comprising nitrogen or carbon monoxide.

The foregoing and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of preferred embodiments thereof as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a schematic block diagram of one embodiment of a laser system in accordance with the present invention utilizing electric discharge excitation of the energizing gas and mixing of the laser gas with a preenergized energizing gas; and

FIG. 2 is a schematic block diagram of another embodiment of a laser system in accordance with the present invention in which the gases used in the laser are excited in, or just prior to entering, the optical cavity.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a source .5 of nitrogen or carbon monoxide energizing gas delivers the gas to an electric excitation means 6. The excitation means 6 may comprise an electric discharge of either the direct current, radiofrequency or microwave variety, an is known in the art. The excitation means 6 excites the energizing gas to vibrational levels. The techniques of electric excitation are well known in the art, and choosing among them is not germane to the present invention.

The vibrationally excited energizing gas passes from the electric excitation means 6 into a laser cavity 7 which also receives a selected cyanogen halide (BrCN, ClCN or FCN) from a source 8 of lasing gas. The lasing gas is preferably introduced into the laser cavity at a relatively low temperature, such as room temperature. Methods of accomplishing efficient mixing of the gas are known in the art. This causes intimate mixing of the vibrationally excited energizing gas with the lasing gas within the optical cavity :so that essentially each molecule of lasing gas which is brought to an upper lasing level of energy will emit photons directly within the laser cavity, therefore avoiding pre-lasing or spontaneous vibrational equilibration processes which would remove molecules of lasing gas from the upper laser level of excitation. Additionally, the use of the mixing configuration illustrated in FIG. 1 may be preferred in order to avoid possible reduction in efficiency and other side effects as a result of a tendency for the lasing gas to undergo chemical reactions or decomposition as a result of the energy imparted thereto within the electric excitation means 6.

The flow of the gas from the source 5., through the electrical excitation means 6 and the laser cavity 7 is caused by suitable pump and effluent control means 9. The pump and effluent control means 9 may provide not only for flow through the system, but also high flow at a relatively low pressure to accommodate the electric discharge involved in the excitation means 6. The pump and effluent control means 9 may also provide for combustion or chemical destruction of the effluent so as to avoid releasing toxic gas. As an alternative, however, a leaktight closed cycle system may be employed if desired without altering the practice of the essential teachings of the present invention.

The technique of mixing the preferably room temperature lasing gas into the excited energizing gas promotes a favorable energy transfer process leading to population inversion as between a lasing level of excitation and lower levels of excitation by the energy transfer process:

001 2219 cmr 010 380 cm.- 1839 emfl...

N(V=)+CICN 000, groundstate)N,(V=0)+ClCN l; upper laser level) These near-resonant exchange processes lead to selective pumping of the 001 level of ClCN at 2,219 cm and a vibrational inversion is established within the ClCN molecules. Within a suitable optical cavity, lasing between the 001 level and several lower vibrational levels in ClCN results. The lasing transitions are, for example:

Approximate wavelength,

Upper level Lower level Engery microns (001; 2219 cm." (100) 714 cm: 1506 em.- 6.6 (001 2219 cm: (020) 784 cm. 1435 cm.- g0 4 The present invention provides laser wavelengths which are i well suited to uses not requiring extensive transmission through the atmosphere.

The efficiency of the laser may be enhanced through the addition of other gases, such as He, H,, and I-I,O which can remove vibrational energy from the lower laser levels.

Similar analysis, eliminated herein for simplicity, illustrates that BrCN and FCN have lasing transitions that may result in radiation at 5.3, 6.2 and 6.6 microns and 5.4, 7.2 and 8.2 microns; respectively.

To produce self-sustained lasing in the flow, the laser cavity should be coextensive with the region of flow containing a finite population inversion between the upper and lower laser levels.

The second embodiment of the invention is illustrated in FIG. 2. This embodiment illustrates that the energizing gas and lasing gas may be mixed in a source 10 prior to being passed through an excitation means, which may in fact consist of a laser cavity with electric excitation means 12, as is known in the art. The outflow of the cavity with electric excitation is passed through a pump and effluent control means I4, as in the case of embodiment of FIG. 1. FIG. 2 illustrates that the excitation of an energizing gas can take place after the energizing gas is mixed with the lasing gas. FIG. 2 also illustrates that the excitation means may be incorporated directly within the laser cavity so the excitation occurs within the laser cavity. FIG. 2 further illustrates, moreover, a configuration which may be utilized wherein the energizing gas is not employed: that is, the source 10 may be a source only of lasing gas, or of lasing gas and a gas suitable to assist in adjusting the cross section of the lasing gas to improve the absorption capability of the lasing gas for direct excitation by the excitation means, without involving the near-resonant collisional energy transfer process with an energizing gas. All of this is known in the art and is not germane to the present invention which is to utilize CICN, BrCN, or FCN as a lasing gas to provide laser radiation of 5 to 10 microns, as described hereinbefore.

Although the invention has been shown and described with respect to preferred embodiments thereof, it should be understood by those skilled in the art that various changes and omissions in the form and detail thereof may be made therein, without departing from the spirit and the scope of the invention.

Having thus described a typical embodiment of my invention, that which I claim as new and desire to secure by Letters Patent of the United States is:

1. In the method of operating a gas laser having a laser cavity, the steps of:

flowing a vibrationally excited energizing gas selected from the group consisting of molecular nitrogen and carbon monoxide through said cavity; and contacting a second gas stream with said energizing gas in 

1. In the method of operating a gas laser having a laser cavity, the steps of: flowing a vibrationally excited energizing gas selected from the group consisting of molecular nitrogen and carbon monoxide through said cavity; and contacting a second gas stream with said energizing gas in the laser cavity, said second gas stream consisting of a lasing gas which is predominantly a cyanogen halide selected from the group consisting of BrCN, C1CN and FCN, whereby the energy of said vibrationally excited energizing gas is transferred to the lasing level of said lasing gas. 